First step to move common accessibility code out of content.

ui/accessibility/ax_tree_serializer.cc

Index: ui/accessibility/ax_tree_serializer.cc
diff --git a/ui/base/models/dialog_model.cc b/ui/accessibility/ax_tree_serializer.cc
similarity index 62%
copy from ui/base/models/dialog_model.cc
copy to ui/accessibility/ax_tree_serializer.cc
index 310bff04c5027dee495cf98b5f4512dda1a3fc46..2e524fa0e77b77fe512f76ef09b9915b547ef885 100644
--- a/ui/base/models/dialog_model.cc
+++ b/ui/accessibility/ax_tree_serializer.cc
@@ -2,11 +2,14 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "ui/base/models/dialog_model.h"
+#include "ui/accessibility/ax_tree_serializer.h"
 
 namespace ui {
 
-DialogModel::~DialogModel() {
+ClientTreeNode::ClientTreeNode() {
+}
+
+ClientTreeNode::~ClientTreeNode() {
 }
 
 }  // namespace ui